As noted in U.S. Pat. No. 7,536,898 issued to Owen, when particle counters measure aerosol concentrations above their operating range, the detectors can become saturated or exhibit undesirable nonlinear behavior. The drawback from these measurement devices arises when they are used to measure aerosol concentrations above the instrument's dynamic range.
To overcome this obstacle, dilution techniques have been employed where the aerosol concentration is diluted by separating the flow path of an aerosol into a filtered path and a non-filtered path. In the filtered path, a filter absorbs the aerosol particles to create relatively pure air which is then mixed with the unfiltered aerosol to create a diluted mix. The diluted mix is then channeled to a particle counter and the collected count data extrapolated to arrive at a particle concentration, which depends on the actual dilution factor created by the diluter. It is often difficult to determine the dilution factor accurately, leading to inaccurate and disputed counts.
The current generation of particle counters is typically designed to measure particulates in clean rooms (also known as “white rooms”) and obtain statistically significant counts based on relatively high sample volumes typically of the order of cubic feet. Consequently, such counters are easily overwhelmed if exposed to high particulate counts. However, it is particularly advantageous to use such particle counters because when operating properly they provide very accurate particle counts. Therefore, a dilution and sampling system that can be used in combination with modern particle counters is highly desired.
U.S. Pat. No. 7,998,252 issued to Huza et al. describes an apparatus and method for certifying a filter in a containment system without decontaminating the containment system prior to certification. The apparatus generally comprises a valve assembly selectable between at least three operational states. A first state prevents flow through a port in housing. A second state fluidly couples the port to test equipment necessary to test a filter disposed within the housing. A third state seals the port but fluidly couples the test equipment to a decontamination system.
U.S. Pat. No. 7,785,408 issued to Jordan Sr., et al describes a particle collector made up of a housing defining an enclosed chamber. An inlet opening in the housing provides fluid communication between a source of gas and particles and the chamber and an outlet opening provides fluid communication between the chamber, and the exterior of the housing. The outlet opening is connected to a pump for drawing gas and particles through the housing from the inlet opening to the outlet opening. A collecting member having an adhesive on at least a portion of the surface is disposed in the chamber between the inlet opening and the outlet opening. The adhesive surface of the collecting member is positioned adjacent to the inlet opening. When gas and particles are drawn through the housing, the inlet opening directs a stream of gas and particles at the surface of the collecting member. Particles having an aerodynamic equivalent diameter of less than about 2.5 μm (2.5 microns) are captured.
While such technologies as described above have some merit there is a need for improved dilution and sampling apparatus to enable, for example, the testing of HEPA filters using a new generation of particulate counters that normally measure particulates in clean rooms.